Synchronize circle.yml with st2 CI process/versioning
Synchronize circle.yml with st2 CI process/versioning

- CircleCI build is triggered only when you push changes to `master` or `vX.Y` like `v0.13` branch
- CircleCI build is never triggered when you push changes in patch `vX.Y.Z` branch like `v0.13.3`
- Package version is always obtained from [`st2common/st2common/__init__.py`](https://github.com/StackStorm/st2/blob/master/st2common/st2common/__init__.py#L16)
- Docker TAG is always:
   - `latest` for `master` branch
   - obtained from version [`st2common/st2common/__init__.py`](https://github.com/StackStorm/st2/blob/master/st2common/st2common/__init__.py#L16) for branches like `v0.13`
   - See: https://hub.docker.com/r/stackstorm/st2api/tags/

You don't need to delete `circle.yml` file in patch version since that, but probably during time there will be small edits like Bintray -> Packagecloud switch or bugfixes.

peak6/st2,dennybaa/st2,lakshmi-kannan/st2,tonybaloney/st2,tonybaloney/st2,lakshmi-kannan/st2,lakshmi-kannan/st2,tonybaloney/st2,Plexxi/st2,StackStorm/st2,dennybaa/st2,punalpatel/st2,nzlosh/st2,peak6/st2,Plexxi/st2,StackStorm/st2,nzlosh/st2,pixelrebel/st2,punalpatel/st2,emedvedev/st2,Plexxi/st2,pixelrebel/st2,peak6/st2,StackStorm/st2,pixelrebel/st2,emedvedev/st2,nzlosh/st2,dennybaa/st2,nzlosh/st2,Plexxi/st2,StackStorm/st2,emedvedev/st2,punalpatel/st2